ИСТИНА

The direct measurements of the magnetocaloric effect (MCE) and the magnetization have been conducted for R2Fe17 (R = Y, Tb, Dy) compounds. The magnetization and the MCE measurements reveal the following peculiarities in R2Fe17 compounds: 1. The wide region of the magnetic phase transition. 2. In contrast to the majority of previously investigated compounds [1], to analyze the dependence of T on magnetization of the sample I, it is necessary to include not only the second power of the magnetization, but also its forth power. Thus the magnetic phase transition to magnetically ordered state in R2Fe17 compounds has a complex character. To describe this transition it is essential to consider not only the thermal fluctuations but also the local fluctuations of the exchange integrals. This leads to the modifications of dependences of T(I) and I(H) in comparison with the classical ferromagnetics. The contributions of fluctuations proportional to the forth power of magnetization play an impotant role.